Free tool to validate that emails from your webapp will pass authentication checks
deliverability.com
deliverability.com
Sender ID is almost the same as SPF, but Microsoft found a way to fk it up. There's info about Sender ID on the site above, and also on http://microsoft.com/senderid
Domainkeys is a little more complex to install, requiring modules or plugins to your mail server. A search should give you enough info to get started.